This invention relates to video signal processing and, more particularly, to an improved method and apparatus for generating a progressively scanned video signal.
In recent years, television display systems capable of displaying larger numbers of lines than standard television, for example, 1125 lines per frame as compared to 525 lines per frame for NTSC television, have become more popular. However, in order to take advantage of this enhanced ability, not only should the display device have greater resolution capability, but the signal to be presented should be in a form to take full advantage of the display device's performance.
Sometimes, a high definition video signal may be available for display. In other situations, a standard television signal (e.g. 525 lines per frame for NTSC) can be converted to a format for display with an increased number of lines per field, such as by using a line interpolation technique.
It has been recognized that using a progressive display format has certain advantages over the standard (for example NTSC) interlaced display format. Compared with an interlaced display, a progressive display eliminates interline flicker, and reduces the visibility of the field-line structure that is noticeable when a viewer makes vertical eye movements.
In systems where an interlaced video signal is converted to progressive format for display, as is done in certain high definition television systems, there has been a need to utilize motion-adaptive processing in an attempt to overcome problems inherent in the conversion. In particular, on the one hand, if information from a full frame (two successive interlaced fields) is combined in generating the progressively scanned frame, there will be motion artifacts that result from part of the information being from an "old" field. On the other hand, if only the current field information is used, the resulting image will have good motion rendition, but suffers a loss in vertical resolution, since only half the available lines are being used. A solution currently employed is to provide both types of information processing, and to also provide motion detection circuitry to control selection of which type of processing is to be used during a particular portion of the image to be displayed. In portions of the picture where there is little or no motion, information from the full frame (including the prior field) is combined, whereas when motion is detected, only information from the current field is utilized. It would be advantageous to be able to eliminate the need for motion-adaptive processing in these types of systems.
As described in my U.S. Pat. Nos. 4,517,597, 4,628,344 and 4,652,909, and in my copending U.S. patent application Ser. No. 07/005,296, now U.S. Pat. No. 4,701,783, an electronic video signal (television signal) can be encoded at reduced bandwidth by lowering the frame refresh rate of the high spatial frequency components, while maintaining the frame refresh rate of at least a portion of the low spatial frequency components at the standard rate. If done in a specified manner, this will not cause substantial degradation in the ultimately displayed image, since human vision cannot perceive changes in high spatial resolution information at as fast a rate as it can perceive changes in low spatial resolution information. Accordingly, as has been previously set forth, an electronic video encoding and decoding system can be devised which takes advantage of this, and other, characteristics of human vision by encoding higher spatial resolution video components to be at a temporal information rate which approximately corresponds to the highest rate actually perceived by human vision for such components; thereby eliminating the need to encode these components at a higher rate, which inherently wastes bandwidth. Also, as shown in the prior patents and copending application, the low spatial resolution information can be generated in a form which is compatible with standard television video, e.g. NTSC video.
It is among the objects of the present invention to provide an improved method and apparatus for generating a high definition video display in progressive scan format which utilizes signals that are in accordance with the system described in my referenced prior patents and application. It is also among the objects of the invention to provide a technique for generation of video in progressive scan format that has application to other types of high definition video systems, as well as to other video systems which would benefit from having a progressive scan format, regardless of their particular original number of lines or resolution capabilities.